A motion detector is a device that detects moving objects, particularly people. A motion detector is often integrated as a component of a system that automatically performs a task or alerts a user of motion in an area. Motion detectors can form an important part of a security, automated lighting control, home control, and other systems.
Motion Detectors usually employ pyroelectric materials to detect the movement of people in a room. A pyroelectric material generates a signal if the incoming heat radiation (from a heat source such as a person's body) changes. Mathematically, the pyroelectric detector generates an electrical signal that follows the time derivative of the incoming heat flux. Thus, if a person enters or leaves the field-of-view (FOV) of the detector, the heat flux changes and a respective signal is generated. The height of the signal is dependent on the temperature of the heat source and the so-called filling factor of the field of view.
The higher the source's temperature and the more the source fills the FOV of the detector, the higher the resulting signal. This signal will exist only for a limited time after a heat flux change, and thus if the heat flux remains constant then no signal is generated. As such it is impossible to detect the presence or absence of a motionless warm object (e.g. a person standing still or having left the sensor area). In a typical implementation, the technology disclosed herein addresses this deficiency.